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oscillation on splitter plate (CFT)

nbohni

We were having many issues the last months with our GC-7200 qtof system. Many have been resolved, but we are left with tailing on later eluting peaks (phthalates, starting at about 250 °C) and oscillations coming from the splitter plate. 

Our system is as follows:

KAS-inlet (Gerstel), 15m column - backflush - 15m column - splitter plate - FID/qtof

The tailing is only on the MS side, and not on the FID. Oscillations are on both channels (and on the actual pressure reading of the corresponding EPC).

We extensively checked for leaks (with a duster), so splitter plate is good. I checked the inertness of the inlet side (including backflush) with the GC degradation mix from Restek (I know that it shows me leaks up to the backflush), so inlet/backflush is fine too. 

Also, analytical columns are in few months only and the system has hardly seen any samples. Transfer line has been exchanged again last week and tailing stayed. (Again, resolution is perfect on the FID!) MS source has been cleaned several times and hardly any samples have been on it since. 

Any ideas what the oscillations on the splitter plate are coming from and how to resolve it?

Any ideas on the tailing of later eluting compounds? (Could it possibly be the transfer line that's not heating evenly? How to check for this?)

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  • 0

    Oscillations - like what?  Pressure reading?  Retention times?  Vacuum readings?   What units and how much?    Is it a purged splitter plate?  If so - - is the purge supplied by an Auxiliary EPC module with the required bleed restrictor mounted on top of the oven ?

    Tailing can be cold spots, too, especially for higher boiling point compounds. Is the GC pushed up tight to the MS transferline so that there is little to no gap ?   What is your transferline temperature?  Removable Ion Source temperature?

  • 0 in reply to paulsalverda

    Oscillations in baseline (TIC) and in pressure reading.

    Blue is FID, red is MS. I recorded the pressure actual from inlet, backflush (EPC6) and splitter plate (EPC4). The pressure starts oscillating after 1 minutes after temperature increase from starting temp. (60 °C). The oscillations in pressure are 0.15 10^-2 of whatever unit it is recorded in. (my reading starts at 1 10^-5, but on the GC it says 4.4 psi. my reading at the end is 4.18 10^-2)

    The splitter plate was mounted by the service technician. I don't see a restriction on top of the oven. There is a connector piece (union) and the tubing disappears towards the EPC. (I cannot check as the Gerstel autosampler is mounted on top.)

    The GC is pushed as tight as possible to the qtof. There are two spacer bars mounted at the qtof and the GC is tight with the spacer bars. This leaves the GC with 1 cm space from the QTOF. 

    Transferline is 300 °C, source temperature is 230 °C. Both temperatures are like this since ever. 

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  • 0 in reply to paulsalverda

    Oscillations in baseline (TIC) and in pressure reading.

    Blue is FID, red is MS. I recorded the pressure actual from inlet, backflush (EPC6) and splitter plate (EPC4). The pressure starts oscillating after 1 minutes after temperature increase from starting temp. (60 °C). The oscillations in pressure are 0.15 10^-2 of whatever unit it is recorded in. (my reading starts at 1 10^-5, but on the GC it says 4.4 psi. my reading at the end is 4.18 10^-2)

    The splitter plate was mounted by the service technician. I don't see a restriction on top of the oven. There is a connector piece (union) and the tubing disappears towards the EPC. (I cannot check as the Gerstel autosampler is mounted on top.)

    The GC is pushed as tight as possible to the qtof. There are two spacer bars mounted at the qtof and the GC is tight with the spacer bars. This leaves the GC with 1 cm space from the QTOF. 

    Transferline is 300 °C, source temperature is 230 °C. Both temperatures are like this since ever. 

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